unit 1: stoichiometry and gases by alex and maria
TRANSCRIPT
Unit 1: Stoichiometry and Gases
By Alex and Maria
Tour of the Periodic Table
– Groups and Periods
• Groups: vertical columns of elements with similar chemical and physical properties
• Periods: Horizontal columns
Element Groups
• Groups 1A: Alkali Metals• Group 2A: Alkali Earth
Metals• Group 3A-4A: unnamed• Group 5A: Pnictogens• Group 6A: Chalcogens• Group 7A: Halogens (salt)• Group 8A: Noble Gases
Naming Ionic Compounds
-Ide -Ite -Ate Per…Ate Hypo-Monatomic NO2
- NO3-
Exceptions ClO2- ClO3
- ClO4- ClO-
OH- SO3- SO4
2-
CN-
•An ionic compound is a metal cation bonding to a non-metal anion•Binary compounds are two nonmetal compounds, like NF3 (add prefix)
Protons, Neutrons, Electrons and Isotopes
• An Isotope is an atom with the same atomic number but different mass numbers because of a difference in the number of neutrons.
• The atomic number of an element is the number of protons
• Neutrons and Protons add up to the mass number of an ion/element
• The number of electrons is determined by the charge of the ion
Example
Element Atomic
#
Mass # # of
Protons
# of Neutrons
# of Electrons
Na 11 23
Na+ 11 23
Na 11 24
11
12
13
1112
11
1011
11
Percent Abundance
• Percent Abundance is the percentage of atoms of each isotope in a sample
• % abundance= • (# of atoms of given isotope) x 100%
(total # of atoms of all isotopes of that element)
Mass Mole Relationships/Percent Composition
• Mass to Mole Relationships:
Mass of A Moles of A Moles of B Mass of B
•Percent Composition=
•(MA/MT) x 100%
Empirical and Molecular Formula
• Empirical Formula: (HINT-Assume 100g sample)
= % composition ÷ (Smallest number of moles)
molar mass
• Molecular Formula:
(Mexp/Memp) x (Elements in Compound)
Example (Empirical Formula)• You have a compound composed of 49.8% C, 5.15% H,
16.49% O, and 28.87% N. Find the empirical formula• 49.48g C x 1 mol C = 4.120mol C = 4 mol C
12.011g C 1.031
• 5.15g H x 1 mol H = 5.110 mol H = 5 mol H 1.0079g H 1.031
• 16.49g O x 1 mol O = 1.031 mol O = 1 mol O 15.9994g O 1.031
• 28.87g N x 1 mol N = 2.061 mol N = 2 mol N 14.0067g N 1.031
C4H5ON2
Example (Molecular Formula)
• If the molar mass for the previous compound is 194.2 g/mol, what is its molecular formula?
• Theoretical molar mass = 4(12.011 g/mol C) + 5(1.0079 g/mol H) + (15.9994 g/mol O) + 2(14.0067 g/mol N)
= 97.0963 g/mol
• 194.2 g/mol ~ 2 96.0963 g/mol
• 2(C4H5ON2) = C8H10O2N4
Balancing Reaction Equations/ Stoichiometry
• To balance a reaction equation be sure to have the same number of elements on the reactant and products side.
• See mass to mole relationship for stoichiometry.
Limiting Reactants/ Percent Yield
• Using stoichiometry find which reactant produces less of either product. This reactant is the limiting reactant.
• (Mexp/Mtheor) x 100%
Hydrates
• Hydrates are compounds which molecules of water are associated with the ions of the compound.
• There is no simple way to predict how much water will be present in a hydrate compound; it must be determined experimentally.
• Mass of Water=Mass of Hydrate Compound – Mass of anhydrous compound
Partial Pressure
• Partial pressure: PA=χAPTotal
Ptotal=((nA+nb+nc…)RT)/V
χA= na/ntotal
• Mole fraction: Ratio of the number of moles of one substance to the total number of moles in a mixture of substances
Ideal Gas Law PV = nRT
P = Pressure (atm) 1atm = 760torr = 760mmHg
V = Volume (L)N = # of molesR = Rate
= .08206 (L∙atm/mol∙K)
T = Temperature (K) K =°C + 273K
m/v = (PM)/(RT) = ρ
GAS….
Kinetic Molecular Theory
• Tiny particles surrounded by much empty space
• Constantly moving• Energy (speed2)
proportional to temperature (T) in Kelvin
• Particles collide without losing energy (preferably an elastic collision)
R.M.S speed/Effusion/Diffusion
• √(3RT)/M = √u2 R= 8.314 J/mol∙K (J=kg∙m2/sec2)T = Temperature (K)M = Molar Mass (kg/mol)
• Effusion is going from a container into a vacuum
• Diffusion is the mixing of two gases• rate1/rate2= √M2/M1
Non-Ideal Gas Law (Van der Waals)
• (Preal+a(n/v)2)(Vreal-bn)=nRT• a= Attractive forces (atm∙L2/mol2)• b= Molecular volume (L/mol)• a(n/v)2 is the correction for intermolecular forces• bn is the correction for molecular volume• a and b are Van der Waals constants
GAS!